US11771471B2 - Growing rods and methods of use - Google Patents

Abstract

Hydraulically expandable spinal rods and methods of use thereof are disclosed. The spinal rod may include a piston rod, a static rod, and a hydraulic pressure chamber for accepting hydraulic fluid and causing the piston rod to move in an expansion direction relative to the static rod. Upon connection of the piston and static rods to a patient's spinal column, the hydraulic spinal rod may be expanded to aid in correction of an underlying spinal deformity.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent application Ser. No. 16/133,069, filed Sep. 17, 2018, which is a continuation of U.S. patent application Ser. No. 14/993,555, filed Jan. 12, 2016, now issued as U.S. Pat. No. 10,092,328, which claims the benefit of the filing date of U.S. Provisional Application No. 62/102,778, filed Jan. 13, 2015, the disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention(s) relates to spinal rods capable of expansion for treating a variety of spinal maladies.

A scoliotic spine is one in which the spinal column is abnormally curved in one or more different directions, causing resultant adverse side effects for the person suffering from the deformity. Surgeons have attempted to correct this abnormal curvature, in some cases, with spinal rods implanted on the patient's spinal column. The spinal rods exert a force on the spinal column to correct and restore the natural curvature thereof. Pediatric scoliosis is a particular spinal deformity that is marred with a common issue—the patient is young and growing and, consequently, the patient's spinal column is growing as well. Thus, any effort to straighten the young patient's spinal column with, for example, a fixed-length rod is likely to encounter a problem. Namely, as the spine grows the fixed-length rod does not allow further thoracic growth in the patient. As a result, expandable spinal rods have developed to accommodate the growing spine in pediatric patients.

Examples of existing expandable spinal rods include magnetic growing spinal rods and mechanically distractible spinal rods. In the case of magnet growing spinal rods, some include a motor actuated by an external magnet to cause separate rod portions to distract and, consequently, lengthen the overall spinal rod. Mechanically distractible spinal rods typically have rod portions that are manually movable relative to each other via a distraction instrument. The rod portions are distracted during multiple different surgeries to cause lengthening of the overall spinal rod and correction of the underlying deformity. Magnetic growing rods suffer from a number of defects, however, namely distraction forces are limited by the strength of the motor used therewith. In addition, the overall rod is not susceptible to common medical imaging techniques (e.g., magnetic resonance imaging (MRI)) used during surgery. Mechanically-distractible rods also suffer downsides, for example multiple invasive surgical interventions are required after the initial, primary surgery to lengthen the rod (e.g., by use of a distractor instrument). The patient therefore suffers from the side effects of multiple invasive surgeries to correct the spinal deformity.

There is therefore a need for an improved spinal rod device usable to correct, for example, scoliosis of the spine.

BRIEF SUMMARY OF THE INVENTION

A first aspect of the invention includes a spinal rod. The rod comprises a first rod portion having an elongate rod section adapted for connection with a first fixation element implanted in a first vertebra, the first rod portion including an internal hollow cavity defined by an internal wall surface, and a second rod portion having an elongate rod section adapted for connection with a second fixation element implanted in a second vertebra, wherein the second rod portion is inserted within the internal cavity of the first rod portion and is axially movable relative to the first rod portion within the internal cavity in an expansion direction. The rod is sealingly engaged to the internal wall surface and thereby defines a hydraulic pressure chamber, the hydraulic pressure chamber being fluidly sealed off from the internal hollow cavity. Further, the spinal rod includes an injection port and a flow channel in fluid communication with the hydraulic pressure chamber, as well as a locking mechanism engageable with the second rod portion, the locking mechanism being effective to lock the second rod portion relative to the first rod portion, wherein the locking mechanism includes a release mechanism allowing for disengagement between the locking mechanism and the second rod portion to permit movement of the second rod portion in a contraction direction opposite the expansion direction.

In an embodiment of this first aspect, the elongate rod section of the first rod portion is fixed relative to its internal hollow cavity. In another example, the injection port and the locking mechanism are in close proximity to each other.

A second aspect of the invention includes a spinal rod. The rod comprises a first rod portion having an elongate rod section adapted for connection with a first fixation element implanted in a first vertebra, the first rod portion including an internal hollow cavity defined by an internal wall surface, and a second rod portion having an elongate rod section adapted for connection with a second fixation element implanted in a second vertebra, wherein the second rod portion is inserted within the internal cavity of the first rod portion and is axially movable relative to the first rod portion within the internal cavity in an expansion direction. The rod is sealingly engaged to the internal wall surface and thereby defines a hydraulic pressure chamber, the hydraulic pressure chamber being fluidly sealed off from the internal hollow cavity. Further, the spinal rod includes an injection port and a flow channel in fluid communication with the hydraulic pressure chamber, as well as a locking mechanism engageable with the second rod portion, the locking mechanism being effective to lock the second rod portion relative to the first rod portion, wherein the injection port and the locking mechanism are in close proximity to each other.

In an embodiment of this second aspect, the injection port and the locking mechanism are adjacent each other on a same side of the first rod portion. Further, the injection port and the locking mechanism may be spaced apart by anywhere from between about 5 mm to about 9 mm. In another embodiment, the locking mechanism is a set screw operable to bear on the second rod portion and lock it relative to the first rod portion, or it is a ratchet and pawl mechanism operable to lock the first rod portion relative to the second rod portion.

A third aspect of the invention includes a method of operating a spinal rod. The method comprises engaging an elongate rod section of a first rod portion of a spinal rod with a first fixation element implanted in a first vertebra of a spine, the first rod portion including an internal hollow cavity defined by an internal wall surface, and engaging an elongate rod section of a second rod portion of the spinal rod with a second fixation element implanted in a second vertebra of the spine, the second rod portion being inserted within the internal cavity of the first rod portion and sealingly engaging the internal wall surface to thereby define a hydraulic pressure chamber. The method also comprises introducing hydraulic fluid into the hydraulic pressure chamber through an injection port of the spinal rod so that the hydraulic fluid acts on the second rod portion and causes it to move in an expansion direction within the internal cavity. Further, the second rod portion is locked relative to the first rod portion after the introducing step. Optionally, the hydraulic fluid is subsequently withdrawn out of the hydraulic pressure chamber.

In an embodiment of this third aspect, the small incision is anywhere from between about 4 mm to about 5 mm in length. In another example, the hydraulic pressure chamber is a remote distance from the injection port, and the method further comprises causing the hydraulic fluid to pass through the injection port, into a flow channel extending between the injection port and the hydraulic pressure chamber, and subsequently into the hydraulic pressure chamber, the flow channel extending substantially parallel to the internal cavity along at least a part of its length.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the subject matter of the present invention(s) and of the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings in which:

FIG.1A is a perspective view of multiple spinal rods according to an embodiment of the present invention, which are implanted side-by-side on a spinal column of a patient;

FIG.1B is a close-up perspective view ofFIG.1A;

FIG.2A is a perspective view of a first embodiment of a spinal rod according to the present invention;

FIG.2B is a side view of a second embodiment of a spinal rod according to the present invention;

FIG.3 is a cross-sectional view of the hydraulic expansion mechanism of the spinal rods shown inFIGS.2A-B;

FIGS.4A-D are side, top, cross-sectional, and perspective views of a piston rod forming part of the spinal rod ofFIGS.2A-B;

FIGS.5A-D are side, top, cross-sectional, and perspective views of a static rod and hydraulic cylinder forming part of the spinal rod ofFIGS.2A-B;

FIGS.6A-D are side, top, cross-sectional, and perspective views of a capture nut forming part of the spinal rod ofFIGS.2A-B;

FIGS.7A-C are side, top, and cross-sectional views of a section of the spinal rods ofFIGS.2A-B;

FIG.7D is a close-up view ofFIG.7C;

FIG.8A is a cross-sectional view of an alternate embodiment of a spinal rod according to the present invention;

FIG.8B is a close-up cross-sectional view of a portion of the spinal rod ofFIG.8A;

FIG.9 is a chart demonstrating the results from testing the spinal rods ofFIGS.2A-B;

FIG.10 is a cross-sectional view of the spinal rod ofFIGS.2A-B in which a pump is connected to the rod;

FIG.11A is a side view of an alternate embodiment of a spinal rod according to the present invention;

FIG.11B is a top view of the spinal rod ofFIG.11A; and

FIG.11C is a cross-sectional side view of the spinal rod ofFIG.11A taken along the axis represented by the dotted line inFIG.11B.

DETAILED DESCRIPTION

In describing the preferred embodiments of the invention(s), specific terminology will be used for the sake of clarity. However, the invention(s) is not intended to be limited to any specific terms used herein, and it is to be understood that each specific term includes all technical equivalents, which operate in a similar manner to accomplish a similar purpose.

Referring toFIGS.1A-B, aspinal column10 is shown with multiplehydraulic rods20 implanted thereon. As illustrated inFIG.1B, eachrod20 is connected at both ends to one or morepedicle screw devices12 implanted in respective vertebra ofspinal column10.Pedicle screw devices12 may be any screw construct commonly known in the art including, for example, pedicle screw constructs that utilize a head with an open channel (referred to as a tulip) for accommodating a portion of a rod, and a threaded screw shank for insertion into a vertebra ofspinal column10. Of course, spinal hooks or other common suitable fixation devices may be used in place of pedicle screws12, as would be recognized by one of skill in the art. In any case, each hydraulicspinal rod20 may be attached topedicle screws12 and expanded at will.Rods20 may use hydraulic technology to achieve expansion, as described in more detail below. Thus,rods20 allow for expansion at selected intervals after initial implantation to accommodate changing surgical parameters (e.g., the growing spine of a pediatric patient suffering from scoliosis).

As shown inFIGS.2A-B,spinal rod20 includes multiple rod portions, namely astatic rod22 and apiston rod60. Both static andpiston rods22,60 may be straight (FIG.2A), pre-bent (FIG.2B) to accommodate the curvature of thespine10 of a particular patient, or may be designed to be bent during surgery (transition fromFIG.2A to2B) to accommodate a particular amount of spinal curvature. As shown inFIG.2B, in one embodiment an end section ofstatic rod22 may be curved upwards (e.g., for fixation to the lumbar spine exhibiting a lordotic curvature) while an end section ofpiston rod60 may be curved downwards (e.g., for fixation to the thoracic spine exhibiting a kyphotic curvature). Of course, static andpiston rods22,60 may be bent in any direction in any combination at the discretion of the surgeon, or at the time of manufacturing.

FIG.3 depicts a cross-sectional assembly view of the hydraulic expansion mechanism ofrod20, the components of which are shown in more detail inFIGS.4A-7B. Referring toFIGS.4A-D,piston rod60 is shown in various views.Piston rod60 has an elongate rod section adapted for connection withpedicle screws12, and anend portion62 having a diameter/dimension larger than a diameter/dimension of the remainder ofpiston rod60. In one embodiment,end portion62 includes one or morecircumferential recesses64, shown best inFIGS.3 and7D, for accommodating one or more seals66 (e.g., O-rings). As shown inFIG.4B,piston rod60 may also be irregular or otherwise non-circular in shape. For instance, it may include aflat section68 running along substantially an entire length (or only a portion) of its elongate section. The irregular shape ofpiston rod60 may ensure that it remains in a rotatably-fixed position once incorporated into the rest of the assembly ofhydraulic rod20. Thus,piston rod60 may be “keyed” in one embodiment.

Static rod22 is shown in detail inFIGS.5A-D. In one embodiment,static rod22 includes an elongate rod section that is connected (in some cases integral or monolithic with) ahydraulic cylinder30. As described above, the elongate section ofstatic rod22 can be bent in any number of directions, during surgery or at manufacturing, to accommodate a particular spinal curvature, or it may be straight.Hydraulic cylinder30 includes aninternal cavity32 that is, in one example, cylindrical in shape.Internal cavity32 is sized to receiveend portion62 ofpiston rod60 to allowpiston rod60 to reciprocate and move axially within internal cavity32 (e.g., for rod-elongation purposes). Movement ofpiston rod60 withininternal cavity32 is limited by a step or stop34 formed ininternal cavity32 adjacent the elongate rod section ofstatic rod22. In one embodiment, the diameter/dimension of an opening defined by step/stop34 is smaller than the diameter/dimension ofend portion62 ofpiston rod60 so thatend portion62 can contact step/stop34 and prevent movement ofpiston rod60 past step/stop34. Beyond such limiting features (and others described with reference to capturenut50 below),piston rod60 is freely movable withininternal cavity32.

Hydraulic cylinder30 also includes a flow injection port or opening38 (FIGS.5B-D) for injection of hydraulic fluid intointernal cavity32. In one embodiment,injection port38 is threaded.Injection port38 leads into aflow channel40 inhydraulic cylinder30 that defines a passageway for allowing fluid (e.g., incompressible hydraulic fluid) to flow withinflow channel40.Flow channel40 is shown best inFIGS.3 and7C-D. Flow channel40 has anopening42 at an end thereof, which leads into ahydraulic pressure chamber44.Hydraulic pressure chamber44 is cylindrical, in one embodiment, and it fluidly communicates withinternal cavity32 ofhydraulic cylinder30. In one case,hydraulic pressure chamber44 forms part ofinternal cavity32. Further,hydraulic pressure chamber44 is sealed at one end via the elongate section ofstatic rod22 connected tohydraulic cylinder30. Thus, fluid (e.g., incompressible hydraulic fluid) can travel throughinjection port38, intoflow channel40, throughopening42, and finally intohydraulic pressure chamber44 ofhydraulic cylinder30 during use. Although not shown,hydraulic rod20 may also include a plug (optionally threaded) for insertion intoinjection port38 when it is not in use. In addition, in anembodiment injection port38 andflow channel38 are welded ontohydraulic cylinder30, although such structures may be integral or unitary in another embodiment.

FIGS.6A-D show acapture nut50, which includes a threaded projectingpart58, achannel52, and a threadedopening54 for receiving a set screw56 (shown inFIGS.7A-D).Channel52 is sized and shaped to receive the elongate rod section ofpiston rod60 so thatpiston rod60 can reciprocate and move withincapture nut50. Likewise, threadedopening54 is sized to receive setscrew56 to allow setscrew56 to be screwed intoopening54 and bear onpiston rod60 to secure it relative to capturenut50 andstatic rod22. In one embodiment,channel52 is also irregularly shaped in the same manner as the elongate rod section of piston rod60 (e.g., it may include a flat portion (not shown) similar to flat section68) so that, whenpiston rod60 is received inchannel52, it is not rotatably movable relative to capturenut50. Thus,channel52 ofcapture nut50 may be “keyed” as well.

An embodiment of an assembled hydraulicspinal rod20 is shown inFIGS.7A-D. As illustrated,internal cavity32 ofhydraulic cylinder30 receives and allows movement ofend portion62 ofpiston rod60 withincavity32. Withend portion62 ofpiston rod60 ininternal cavity32,capture nut50 may be screwed into threadedend36 ofhydraulic cylinder30 to permit movement ofpiston rod62 ininternal cavity32 betweenstop34 and projectingpart58 ofcapture nut50. Ascapture nut50 is secured to threadedend36,piston rod60 is rotatably secure relative to capturenut50,static rod22, and hydraulic cylinder30 (e.g., due to the “keyed” nature ofpiston rod60 and channel52). In other words, the irregular shapes ofpiston rod60 andchannel52 ofcapture nut50 precludes or at least substantially inhibits relative rotational movement betweenpiston rod60 and capturenut50.Piston rod60 is therefore capable of moving axially withininternal cavity32 ofhydraulic cylinder30 to multiple different positions, without unwanted rotation, thereby allowing expansion ofspinal rod20 to different lengths.Seals66 onend portion62 ofpiston rod60 may also sealingly close off portions ofinternal cavity32 to the right and left ofend portion62, as shown inFIGS.7C-D, and allowend portion62 andpiston rod60 to move smoothly (without substantial friction) ininternal cavity32. In one embodiment,spinal rod20 may be effectively lengthened by about at least one-hundred millimeters (100 mm) in successive intervals, as determined by the surgeon (e.g., successive ten millimeter (10 mm) lengthening procedures). In another embodiment, thespinal rod20 may be lengthened by about anywhere between forty millimeters (40 mm) to two-hundred millimeters (200 mm) in successive intervals, as determined by the surgeon. After a lengthening procedure, setscrew56 can be used to lockspinal rod20 in its expanded position (e.g., it may bear uponpiston rod60 to lock it relative to static rod22).

In use, a surgeon first makes an incision into a patient's back and then implants one or morespinal rods20 on the patient's spinal column10 (e.g., via attachment of static andpiston rods22,60 with pedicle screws12). Static andpiston rods22,60 may reside in the tulip portion of pedicle screws12 and be affixed with a set screw or other fixing device (e.g., a cam mechanism), as is common, to prevent relative movement between static andpiston rods22,60 and pedicle screws12. As shown inFIG.2B,rods22 may be contoured during surgery or at manufacturing to conform to the shape of the particularspinal column10 at issue. In an embodiment, a patient-specificcontoured rod20 may be created by way of first computer imaging the patient'sspinal column10 and then manufacturing arod20 with a particular curvature to meet the patient's specific anatomy. Thus,rods22 may fit the particular patient's needs. At initial implantation, eachrod20 may be pre-configured in length to fit the patient'sspinal column10, and its curvature, or the surgeon may utilize the hydraulic mechanisms present in eachrod22 to initially setrods22′s length. As an example, eachrod22 may be selected from a kit ofrods22 having different lengths so as to fit the particular patient's anatomy, or arod22 may be selected and then hydraulically actuated to achieve an initial proper fit for the patient.

In the latter scenario discussed above, the surgeon would utilize asyringe device16 of the type shown inFIGS.1A-B to expandhydraulic rod20 to its initial fit. In an embodiment,syringe device16 attaches toinjection port38 ofhydraulic cylinder30 so as to establish a secure connection therebetween (e.g., via threading on a distal end ofsyringe device16 and the threading of injection port38). Subsequently, the surgeon may force a hydraulic fluid, such as an incompressible, biocompatible fluid (e.g., preferably sterile water or saline fluid, but also other biocompatible fluids such as liquid antibiotics, blood, or oils) under pressure intoinjection port38. The fluid may flow intoinjection port38, throughflow channel40, into and throughopening42, and finally intohydraulic pressure chamber44 where the fluid can exert a force againstend portion62 ofpiston rod60. Due toseals66surrounding end portion62, and the attachment ofstatic rod22 tohydraulic cylinder30, a sealedhydraulic pressure chamber44 is created therebetween. The force generated by the surgeon in usingsyringe16 can therefore be translated through the hydraulic fluid and directly act onend portion62 ofpiston rod60.

In one example,syringe16 may include a powered or manual pump mechanism for forcing hydraulic fluid under pressure intoinjection port38, orsyringe16 may include other manual means for undertaking the same (e.g., a plunger and a rotating screw mechanism for advancing a plunger ofsyringe16 under pressure). Thus, the surgeon is afforded either a powered ormanual syringe16 to force hydraulic fluid under pressure into hydraulic cylinder30 (specifically hydraulic pressure chamber44). The surgeon can consequently cause movement ofpiston rod60 withininternal cavity32 ofhydraulic cylinder30 by a desired amount to cause expansion ofspinal rod20, in terms of its length.

A specific embodiment illustrating a mechanical pump mechanism for expansion ofspinal rod20 is shown inFIG.10. Although onlyrod20 is shown inFIG.10, it is equally contemplated that the pump mechanism described in connection withFIG.10, or any other pump mechanism disclosed herein, could be used withrod120 ofFIGS.8A-B (detailed below). As illustrated inFIG.10, pump200 is a mechanical pump that includes ahollow pump body210, aspring212 disposed inbody210, and acap214 andpiston216 surroundingspring212.Pump body210 includes ahollow bore218 for containing an incompressible fluid of the type described above, andpiston216 sealingly contacts the walls ofbody210 definingbore218 so as to be able to drive the incompressible fluid out ofpump200. In this regard,cap214 is, in an embodiment, threaded intopump body210 and provides a stop forspring212 at a first section ofbody210, whilepiston216contacts spring212 at a second section ofbody210. Incompressible fluid is disposed beyondpiston216 withinbore218, andpiston216 acts on the fluid due to force generated byspring212. In other words,spring212 is compressed to some extent betweenpiston216 andcap214 so as to forcepiston216 in a downward direction withinbore218 against the incompressible fluid. In an embodiment,spring212 is capable of exerting anywhere between about 0-1000 N of force onpiston216. As further shown inFIG.10,pump body210 is fluidly connected with aconduit220, which extends through anopening226 inpump body210.Conduit220 is attached (e.g., integral or monolithic) to aflange222, which sits withinbore218 and is in turn in contact with a sealingmember224 disposed at a bottom part ofpump body210. The dimension/diameter offlange222 is larger than that of opening226 so thatconduit220 is securely retained inpump body210. In addition, an end part ofconduit220 may also include a threadednut228 for engagement withinjection port38 ofrod20.

In use, pump200 may cause incompressible fluid to expandspinal rod20, much in the same way as described above (and below in connection with rod120), through the action ofspring212 forcingpiston216 downwards against the incompressible fluid. Movement ofpiston216 causes the incompressible fluid to travel throughconduit220 and intospinal rod20 to expandrod20 in the manner set forth above. Alternately stated,spring212 is designed so that an appropriate amount of force is borne onpiston216 throughoutrod20′s lifecycle, thereby generating enough distraction force between static andpiston rods22,60 to cause the patient's spinal deformity (e.g., scoliotic curvature) to be corrected. As the patient grows, for example in the case of an adolescent patient,rod20 withpump200 attached can expand along with the patient's growth and exert a sufficient force on the patient's spinal column to cause correction of the deformity/curvature. As an example,rod20 in use withpump200 may be configured to initially exert a first distraction force of up to 1000 N on an adolescent patient's spinal column at implantation, decreasing progressively to a second distraction force of 0 N duringrod20′s lifecycle. The first and second distraction forces mentioned above are, of course, sufficient to cause medically appropriate correction of the patient's deformity (e.g., straightening of the patient's spine).Spring212 can also alternatively be designed to provide a constant distraction force forspinal rod20 over time.

It should be noted that, although a mechanical pump has been described above, it is equally contemplated that an electrical pump, osmotic pump, or other type of low flow rate static pump could be used. In each of the aforementioned cases, the pump may also be implanted sub-dermally in the patient and, where applicable, actuated via an external actuation device. As an example, an induction, magnetic, or other internal motor could be used with the pump, which is actuated via an external actuation device to cause actuation of the pump andspinal rod20's expansion. Using an electric pump as an illustrative case, the pump may have an internal electric motor that is capable of being actuated through induction or through other wireless means (e.g., a receiver). The system may also include an external controller for actuating the induction motor or other wireless mechanism causing the electric pump/motor to function. In an example, an RF transmitter or other like device could be incorporated into the controller for communicating with the above-mentioned wireless means.

To determine the appropriate amount of expansion, common medical imaging techniques (e.g., MRI, fluoroscopy, etc.) can be used to viewspinal rod20 after it has been expanded by some amount. Alternatively, a certain amount of force and pressure can be correlated to a particular lengthening forspinal rod20. Ifrod20 is expanded by an appropriate amount (a 10 mm expansion is common), the surgeon can then lockpiston rod60 viaset screw56 and fix the length ofrod20. In particular, ascrew driver14 of the type shown inFIGS.1A-B may be used to rotate setscrew56 and cause it to bear againstpiston rod60 to fix the overall length ofrod20. Withrod20 in position, the surgeon can then complete the surgery and close any incisions therefor. Of course, as noted above, the surgeon may alternatively be provided with arod20 that does not require alteration at initial implantation and only requires length expansion during subsequent surgical interventions. In one case, to finish expansion ofspinal rod20, the surgeon evacuates all, substantially all, or simply a majority of hydraulic fluid fromhydraulic pressure chamber44 androd20 after locking. Asrod20 is locked via setscrew56, it is not necessary to keep constant hydraulic pressure to maintain the positioning of static andpiston rods22,60. In such an embodiment, a threaded plug (not shown) may be used to fluidly seal offinjection port38 after all or the necessary amount of hydraulic fluid is evacuated fromrod20.

After initial implantation, of either a lengthened ornon-lengthened rod20, the surgeon is afforded an opportunity to periodically lengthenhydraulic rod20 using the same process described above. Thus, hydraulic fluid can be inserted intoinjection port38 to cause expansion ofrod20 and correction of the underlying spinal deformity (e.g., scoliosis). In these expansion procedures,rod20 may be unlocked at some point to allow for expansion, and then the surgeon may re-lockrod20 and optionally withdraw the necessary amount of (e.g., all) hydraulic fluid from the system to finish the procedure. Thus, a growingspinal column10 can be accommodated viarod20.

The aforementioned surgical interventions (lengthening procedures) are not as demanding as typical procedures since only a small incision needs to be made to accessinjection port38 and cause expansion ofspinal rod20. In some cases, the incision may be anywhere from about three to about six millimeters (3-6 mm) in length, and most preferably about four to about five millimeters (4-5 mm). As such, a pediatric patient with a growing spine can return to the surgeon on a periodic basis (e.g., every six (6) months) to confirmspinal rod20's effectiveness and, if necessary, obtain an adjustment/lengthening. In some cases, the lengthening may be by about ten millimeters (10 mm) at each surgical intervention. At the culmination of the lengthening procedures, a fusion procedure may take place (if indicated) to ensure the patient'sspinal column10 remains in the corrected position. Thus,rod20 presents an effective way to allow for expansion via non-invasive, periodic surgical interventions. In addition, in cases where a pump is implanted sub-dermally, surgical interventions for rod expansion post initial implantation are not necessary as rod20 (or120) expands on its own (e.g., viaspring212 when using pump200), or through the use of an external actuation device, without surgical intervention.

FIG.9 shows a graph representing results obtained from testing an embodiment of aspinal rod20, as described above. The graph demonstrates that peak forces of six hundred Newton's (600 N) were observed upon hydraulically expandingspinal rod20, as well as lower forces. Thus,spinal rod20 is capable of exerting forces of up to six hundred Newton's (600 N) or more on a patient's spinal column to correct the curvature thereof. Clinically, the amount of force required to expand a spinal rod, in situ, increases with each surgical intervention. Peak forces needed at, for example, the tenth lengthening procedure might be on the order of six hundred Newton's (600 N), while the first and third lengthening procedures might be one-hundred and forty (140 N) and one-hundred and sixty five (165 N) Newton's, respectively. Other existing expandable spinal rods have difficultly achieving the peak forces required for later-stage lengthening procedures, but due to the construction of the presentspinal rod20, peak forces needed for late-stage lengthening procedures can be achieved. The graph shown inFIG.9 also does not represent failure testing forspinal rod20, and rather it merely reflects testing to establish clinical efficacy. As such,rods20 may exert even greater loads than those exemplified inFIG.9 and still be within normal operating parameters. As an example, greater loading ofrod20 is possible using the pump mechanism ofFIG.10, as detailed above.

An additional benefit ofrod20 is the minimal or no surgical intervention that is required at each lengthening procedure. If surgical intervention is required, the minimally-invasive nature thereof is due in part to the closeness ofinjection port38 and set-screw opening54, in terms of proximity/location. Indeed, in oneembodiment injection port38 and set-screw opening54 are spaced apart by about eight millimeters (8 mm). In another case, the distance may be anywhere from about five millimeters to about nine millimeters (5-9 mm). This small separation allows only a minimal incision to be made in the patient (e.g., of the size mentioned above) to gain access to both components ofspinal rod20 needed for expansion. In other words, as reflected by the closeness ofscrew driver14 andsyringe16 inFIGS.1A-B, only a small incision is needed to access the components necessary to expand rod20 (i.e.,injection port38 and set screw56). Thus, only a small incision is needed to affect expansion ofrod20, leading to only minor surgical trauma/side effects for the patient. In the case of using a pump mechanism, typically no surgical intervention is required. An additional benefit torod20 is that the patient will have increased thoracic growth because of the constant distraction pressure versus repetitive distractions performed at separate surgeries.

In an alternate embodiment, it is also possible to constructrod20 so thatinjection port38 andopening54 are co-axial (e.g., they are the same opening) to experience possible greater benefits. For instance, capturenut50 may not includeopening54 and insteadinjection port38 may serve as a set-screw opening in addition to an injection port opening. In this case,injection port38 would communicate directly withinternal cavity32 so that setscrew56 could be screwed intoinjection port38 and bear onpiston rod60. Further, setscrew56 could itself include an opening that, when aligned appropriately withflow channel40, would create a fluid flow channel through set screw56 (in particular through its opening), intoflow channel40, throughopening42, and intohydraulic pressure chamber44. In such a modification,internal cavity32 could be sealed off from fluid interaction during an expansion procedure, for example because the end ofset screw56 is closed and fluid flow would only be possible through the opening inset screw56 and intoflow channel40. Also, in such an embodiment the driver-engaging portion ofset screw56 may include threads for interacting with, for example, distal end ofsyringe16. In this case,syringe16 andscrew driver14 may be made into a combination instrument. In any case, the benefits of the close proximity betweeninjection port38 and set-screw opening54 are apparent, as are the benefits resulting from an embodiment in which only a single opening is provided, as discussed above. Namely, only a small incision is needed to access such components and cause expansion ofrod20. Thus, the patient experiences less trauma and/or negative side effects.

An alternate embodiment of aspinal rod120 is shown inFIGS.8A-B. Like numerals refer to like elements in this embodiment, but with numbers in the 100 series, and only the differences betweenspinal rods20,120 will be discussed.

Spinal rod120 includes a different lengthening/locking structure as compared tospinal rod20. In particular, as shown inFIG.8A and in close-up inFIG.8B, a ratcheting mechanism is used to achieve lengthening and locking ofpiston rod160. In one embodiment, the ratcheting mechanism includes acapture nut150, which has anopening154 leading to aninternal cavity157. Inside ofinternal cavity157 is apawl151 having one or more teeth that are sized to interact withteeth161 formed onpiston rod160.Pawl151 rests on aspring153 disposed at a bottom end ofinternal cavity157, which biases pawl151 in the direction ofopening154. In an embodiment,spring153 includes a set oflegs159 that rest, respectively, on a surface ofpawl151 and a floor defininginternal cavity157. In betweenlegs159 is a curvilinear segment forming the remainder ofspring153. Aspawl151 acts onlegs159 and the remainder ofspring153,spring153 is caused to flex and allow for movement ofpawl151. As such,piston rod160 can move in one direction due to movement ofpawl151 againstspring153 and out of engagement withteeth161. As an example,pawl151 can flex againstspring153 and allow movement ofpiston rod160 in an expansion direction (left inFIGS.8A-B), but not a contraction direction (right inFIGS.8A-B). Thus, asrod120 is hydraulically expanded (e.g., in the manner discussed above with respect to rod20),pawl151 can engagesuccessive teeth161 onpiston rod160 and ensure thatpiston rod160 is locked relative tohydraulic cylinder130 andstatic rod122. In this embodiment, a set screw mechanism is therefore not needed.

If, for some reason,piston rod160 is elongated too far,rod120 also includes arelease mechanism155 for allowing movement ofpiston rod160 in the contraction direction.Release mechanism155 may constitute an integral or unitary part of pawl151 (e.g., a top portion or button thereof). Indeed,pawl151 may be a tubular or cylindrical structure with apassageway163 foraccommodating piston rod160, which is slightly larger in diameter/dimension than a diameter/dimension ofpiston rod160. As such,release mechanism155 ofpawl151 may be depressed by a user against the action ofspring153 to disengage the tooth or teeth ofpawl151 from theteeth161 ofpiston rod160. This would allowpiston rod160 to move in the contraction direction, as needed. For example, a user may utilize a tool to depressrelease mechanism155 and consequently allow disengagement ofpawl151 fromteeth161 to permit movement ofpiston rod160 in the contraction direction. Thus, if needed (e.g., ifrod120 is lengthened by too great an amount),release mechanism155 may be used and the length ofrod120 may be shortened. While not mentioned above, it is to be appreciated that this type of contraction/shortening is also possible with setscrew56. As noted above in connection with the various pump mechanisms,rod120 is also usable with any pump mechanism disclosed herein, including any sub-dermal pump, for expansion of rod120 (e.g., to maintain a constant or variable distraction force for rod120).

Yet another alternate embodiment ofspinal rods20,120 is shown inFIGS.11A-C. Like numerals refer to like elements in this embodiment, but with numbers in the 300 series, and only the differences betweenspinal rods20,120 and320 will be discussed.

Althoughrod320 is shown as being more closely aligned with the structure ofrod20 thanrod120, in that no ratchet mechanism is used, it should be recognized that the followingdiscussion concerning rod320 is equally applicable torod120 in the context ofrod120′s ratchet mechanism. Put simply, the concepts and different structures ofrod320 can be utilized withrod120 and its ratchet mechanism as well.

Rod320 includes the same structures (e.g.,internal cavity32,flow channel40,capture nut50, seals66, etc.) asrod20, although a number of those structures are not designated by reference numerals inFIGS.11A-C. For simplicity's sake, only the distinctions betweenrod20 androd320 are highlighted.Rod320 is different fromrod20 in thatrod320 has a curved shape along its length, including a curvature forhydraulic cylinder330. Such curvature produces, for example, a curved internal cavity and a curved flow channel (both not designated by a reference numeral) extending tohydraulic pressure chamber344. In particular, the internal cavity ofhydraulic cylinder330 is curved along its length due to the curvature ofhydraulic cylinder330, and the flow channel leading tohydraulic pressure chamber344 is likewise curved.

In an embodiment,piston rod360 ofrod320 is curved upwards for fixation to the lumbar spine exhibiting a lordotic curvature,hydraulic cylinder330 is curved upwards and transitions to less of an upward curve as it approaches static rod322 (e.g.,hydraulic cylinder330 has a variable curvature), andstatic rod322 is curved downwards for fixation to the thoracic spine exhibiting a kyphotic curvature. In the end, the curvature ofpiston rod360,hydraulic cylinder330, andstatic rod322 may follow anaxis370 that forms a substantially S-shaped curve. In an alternate embodiment,hydraulic cylinder330 may transition from less of an upward curve to a downward curve as it approachespiston rod322. Of course, as recognized above, the curved nature ofrod320 may be utilized in connection withrod120 and its ratchet structure, although not described in detail herein.

In the devices shown in the figures, particular structures are shown as being adapted for use in the implantation, distraction, and/or removal of hydraulically-expandable spinal rods according to the present invention(s). The invention(s) also contemplates the use of any alternative structures for such purposes, including structures having different lengths, shapes, and/or configurations. For instance, although the disclosure references threaded structures in many cases (e.g., threadedend36,136 ofhydraulic cylinder30,130, threadedinjection port38,138, etc.), it is equally contemplated that non-threaded alternative engagement structures can be used. In particular, press-fit, bayoneted engagement structures, and/or ball-and-detent engagement structures may be used. In short, provided engagement between the referenced structures is achieved, any connecting structures can be used.

Further, while the hydraulic mechanism herein is described as ahydraulic cylinder30,130 it is not necessarily tied to that shape and any suitable shape can be used (e.g., square, rectangular, triangular, hexagonal, etc.) The same is true forhydraulic cylinder30,130'sinternal cavity32,132 and other components (e.g.,end portion62,162 ofpiston rod60,160 fitting withinsuch cavity32,132).

In addition, it is contemplated that while therods20,120 herein are described as being formed from multiple components,such rods20,120 may instead be 3D printed to provide for less components and more unitary structures. For example,static rod22,122 andhydraulic cylinder30,130 may be 3D printed as a single component, along withinjection port38,138 and flowchannel40,140 (which are welded tohydraulic cylinder30,130 in the main embodiment).

As yet another example, while certain steps of the above-described method(s) are discussed in a particular order, it is to be understood that the order may be altered in any manner suitable to implant or distract therods20,120 described above. Thus, the order of steps for the method(s) is not essential, and such order may be varied or changed in any manner considered suitable by one of skill in the art.

Although the invention(s) herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention(s). It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention(s) as defined by the appended claims.

It will also be appreciated that the various dependent claims and the features set forth therein can be combined in different ways than presented in the initial claims, and that the features described in connection with individual embodiments may be shared with others of the described embodiments. In particular, as understood by one of skill in the art, the features of any dependent claim may be shared with a separate independent or dependent claim, to the extent feasible.

Claims (18)

The invention claimed is:

1. A method of expanding an implanted spinal rod comprising:

introducing hydraulic fluid into a hydraulic pressure chamber of a first rod portion of the spinal rod so that the hydraulic fluid causes a second rod portion to move in a first direction relative to the first rod portion, wherein the second rod portion has an elongate rod section having a longitudinal length with a constant cross-sectional shape, the cross-section being transverse to the longitudinal length; and

moving a locking member along an axis that intersects a longitudinal axis of the second rod portion such that the locking member engages with a tapered surface of the first rod portion to prevent the second rod portion from moving in a second direction opposite the first direction.

2. The method ofclaim 1, wherein during the engaging step, the locking member bears on the second rod portion.

3. The method ofclaim 2, wherein during the engaging step, the locking member moves in a first locking direction along an axis that intersects a longitudinal axis of the second rod portion.

4. The method ofclaim 3, further comprising the step of moving the locking member in a second releasing direction opposite the first locking direction to allow the second rod portion to move in the second direction.

5. The method ofclaim 1, wherein the introducing step includes pumping fluid into the hydraulic pressure chamber.

6. The method ofclaim 5, wherein fluid is pumped through an osmotic pump.

7. The method ofclaim 5, further comprising the step of sub-dermally implanting a pump in a patient.

8. The method ofclaim 1, wherein during the introducing step, as the second rod portion moves relative to the first rod portion, a size of the hydraulic pressure chamber changes.

9. A method comprising:

introducing hydraulic fluid into an internal cavity of a first rod portion of the spinal rod so that the hydraulic fluid causes a second rod portion to move in an expansion direction relative to the first rod portion, wherein the second rod portion has an elongate rod section having a longitudinal length with a constant cross-sectional shape, the cross-section being transverse to the longitudinal length; and

moving a locking member in a first locking direction along an axis that intersects a longitudinal axis of the second rod portion so that the locking member bears on the second rod portion to prevent the second rod portion from moving in a retraction direction, opposite the expansion direction.

10. The method ofclaim 9, wherein the second rod portion sealingly engages an internal wall surface of the internal cavity thereby defining a hydraulic pressure chamber that receives the hydraulic fluid.

11. The method ofclaim 9, further comprising the steps of:

engaging the first rod portion with a first fixation element implanted in a first vertebra of a spine;

engaging the second rod portion of the spinal rod with a second fixation element implanted in a second vertebra of the spine.

12. The method ofclaim 9, further comprising the step of moving the locking member in a second releasing direction, opposite the first locking direction.

13. The method ofclaim 10, wherein the introducing step includes pumping fluid into the hydraulic pressure chamber.

14. The method ofclaim 13, further comprising the step of moving the second rod portion in the retraction direction.

15. A method comprising:

osmotically pumping hydraulic fluid into an internal cavity of a spinal rod to cause a second rod portion to move in a first direction relative to a first rod portion, wherein the second rod portion has an elongate rod section having a longitudinal length with a constant cross-sectional shape, the cross-section being transverse to the longitudinal length; and

moving a locking member along an axis that intersects a longitudinal axis of the second rod portion such that the locking member engages with a tapered surface of the first rod portion to prevent the second rod portion from moving in a second direction opposite the first direction.

16. The method ofclaim 15, wherein the second rod portion sealingly engages an internal wall surface of the internal cavity thereby defining a hydraulic pressure chamber that receives the hydraulic fluid.

17. The method ofclaim 16, wherein the pumping step includes pumping fluid into the hydraulic pressure chamber.

18. The method ofclaim 15, further comprising the steps of:

engaging the first rod portion with a first fixation element implanted in a first vertebra of a spine;

engaging the second rod portion of the spinal rod with a second fixation element implanted in a second vertebra of the spine.

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